am I dumb?

so my SO cheated on me and ended up having a son with the girl, which broke my heart so much! we have a daughter together and he also has a daughter from another previous relationship before me. Am I stupid for staying? Although it killed me I had to forgive him not for him but for me, we talk to a church counselor about our relationship and have both moved on from the situation. I can't forget what he's done but I know how sorry he is and although it questions trust in my eyes I still love him and we share a family together. the girl keeps his son from him and I bought things such as car seat clothes and etc for him and she refuses to let him see the baby. I accepted what has happen. Please tell me I'm not dumb for staying